The present invention relates to improvements in sheet feeding devices for copiers, printers and other equipment, and it relates more particularly to an improved sheet feeding device for successively dispensing individual sheets from a cassette containing a stack of the sheets.
Separating pawl members are usually used for dispensing individual flexible copy sheets from a stack of the sheets. When the uppermost sheet of the stack starts to advance under the action of a feeding member, the separating pawl members engage the sheet at the opposite corners of its leading end and temporarily restrain the sheet from advancing to bend or buckle the sheet, causing the uppermost sheet only to pass over the pawl members under the influence of the resilient force of the sheet resulting from the bending.
Although the buckled form of the sheet varies with the material and thickness of the sheet and with the distance between the feeding member and the separating pawl members, the sheet will be discharged obliquely or along with another sheet, or will fold or wrinkle when not deformed to the shape required for the sheet to pass over the pawl members.
There is described in U.S. Pat. No. 3,647,204, issued Mar. 7, 1972 to J. Sato, an arrangement for bending sheets of different sizes to approximately the same shape, which arrangement includes pairs of rollers serving as feeding members and being fixedly mounted on a shaft, each pair of rollers being positionable at a substantially constant distance from separating pawl members when the pawl members are shifted for sheets of different sizes. Thus, the mechanism described in the aforesaid patent to Sato functions to assure an approximately constant bent form for sheets of different sizes but does not so function for sheets of different physical qualities or thicknesses.
On the other hand, the sizes of sheets vary from country to country. In Japan and West Germany, for example, sheets of sizes in A and B series are usually used, while in the U.S. sheets of letter size, legal size and computer size are generally employed. As a consequence, even when copiers of the same type are manufactured, sheet feeding mechanisms, which differ in the arrangement of the rollers for use in different countries, must be provided in the Sato device in accordance with the sheet sizes used in the respective country. Accordingly, several different feeding mechanisms must be designed and fabricated, leading to a significant cost increase and necessitating a complex assembling procedure.